METHOD FOR ASSEMBLING DURING MOLDING PARTS OF DIFFERENT PLASTIC COMPOSITION

Abstract: A new method for manufacturing by molding a component, composed partly of a hard thermoplastic material and partly of a soft elastomer material, is proposed. According to the method the first part (53) of thermoplastic material is first formed, then this first part (53) is placed in a mold capable to receive an elastomer material and consequently the second part (51) is formed by injection molding. Simultaneously the surface (58) of the first part (53) is engaged with the surface (54) of the second part (51) and said surface (58) of the first part is subjected to the injection temperature and pressure of the soft elastomer and causes to soften it and to fuse it to said surface (54) of the second part. The method is illustrated on the hand of a valve.

Description: DESCRIPTION Method for assembling during molding parts of different plastic composition The present invention relates to a method for assembling, during molding, parts of different plastic composition and in particular thermoplastic material with an elastomer. Thermoplastic materials are used these days for a very large variety of components for devices, apparatuses, machines, etc... For some components hard thermoplastic material, used for its wear resistant character, is combined with a softer material, used for instance for its resilient or elastic character. When components, constituted of two parts each made of another type of synthetic material and each having a specific form, have to be manufactured it is of common practice to fabricate by extrusion, molding, etc . , the parts separately and to assemble them by using adhesives or other attachment means such as bolts and the like. When the shape of the parts is such that the tolerances are small or alignment is important, assembling such parts remains a difficult and time consuming operation. It is an object of the present invention to propose an improved method for manufacturing by molding a component composed partly of a hard thermoplastic material and partly of a soft thermoplastic elastomer material. The method according to the invention comprises following steps: - forming first the part of hard thermoplastic material; - placing the first part in a mold capable to receive the soft elastomer material; - injection molding the soft elastomer (second) part and simultaneously engaging the surface A (to be assembled to the second part) of the first part to the surface B (to be assembled to the first part) of the second part and subjecting the surface A to the injection molding temperature and pressure whereby the surface A is softened and consequently both surfaces A and B are fused together. By first fabricating the first part and then the second part and by assembling in the mold during fabrication of the second part both parts by fusion, it becomes possible to make components constituted of different materials and of very complicate form with great accuracy. The injection temperature and pressure of the elastomer material will be chosen by the man skilled in the art in function of the type and composition of the thermoplastic material. As hard thermoplastic material, the well known hard polymers and copolymers with linear chain can be handled according to the method of the invention and there is no limitation on the composition of the thermoplastic material which may be reinforced for instance with glass or other fibers. Preferred hard thermoplastic materials particularly suitable for use with the invention are glass filled polypropylene, acrylonitrile-styrene copolymer as for instance acrylonitrile-butadiene- styrene and hard polyvinylchloride. All soft elastomers which can be formed by molding can be used according to the invention, however preferred elastomer particularly adapted for the invention are synthetic rubbers, silicone rubbers, butadiene polymers or copolymers, soft vinyl or urethane polymers, polyethylene or sulfonated polyethylene polymers, soft styrene copolymers as for instance a copolymer of styrene-ethylene and of butylene-styrene. A specific application of the invention comprises a component having a movable part, made from hard thermoplastic material and a part assuming a tightness function made from a soft elastomer, such components can be parts of several devices, such as valves, membranes, tools, moving parts in machines etc... For the sake of clarity the invention will be further described on the hand of a device including a component made of a hard thermoplastic part and a soft elastomer part. The device used in this description is a valve of the type described by applicant in its US Patent 4,535,807. As described hereunder in more details with the description of the drawings, the valve comprises a housing which includes a central passageway connectable to the vent pipe of a plumbing system and an annular port connectable to atmosphere with interposed there between a specific component (valve head) constituted of two different plastic materials. The valve further includes a valve seat which consists of concentric generally circular upstanding beads which define between them the inlet port connected to the atmosphere and also a valve plate which consists of a generally circular ring made of a soft elastomer material and sized to cover the ring-like port formed between the above-described generally circular beads. The valving plate has an upper surface facing away from the valve seat and a lower seat engaging surface overlying the valve seat. The lower surface has affixed thereto a valve guide consisting of a hard plastic ring having a plurality of downwardly depending guide lugs, each one of which has an internally facing slot therein. The outer wall of the support structure of the valve body for the inner seat bead has a corresponding plurality of outwardly extending fins sized to enter the slots of the guide lugs so as to firmly and smoothly guide the valving plate in its upward and downward movements away from and toward the valve seat, respectively. The embodiment of the present invention consists in the specific manner of assembly of the valving plate to the valve guide. As pointed out in the preamble of this description, use of adhesives to hold the valving plate and valve guide together has occasionally resulted in adhesive breakdown in the humid, corrosive environment in the plumbing system. Furthermore, other means of attachment such as, for example, bolts are equally ineffective as providing locations where corrosion and failure of the valve may take place. Thus, according to the present invention, the valving plate is assembled to the valve guide by the different characterizing steps which are inexpensive, highly effective, reliable, reproducible and exact in position. The inventive method of assembly consists of forming, by molding the valve guide from hard thermoplastic material. The surface of the mold engaging the top surface of the valve guide is sand blasted to provide a rough top surface for the valve guide. The molded guide is then removed from its mold and placed in another second mold where the valving plate, made of a soft elastomer, is injection molded and engaged or attached to the top surface of the valve guide. The top of the valve guide is melted when subjected to the temperature and pressure of the injected elastomer and a thin layer on the top surface of the valve guide fuses with the engaging surface of the valving plate so that when the combined valving plate and valve guide are subsequently cooled, a one piece structure results. Preferably the second mold is sand blasted prior to receive the soft elastomer to enhance release from the mold without deforming the valve plate. As such, it is the object of the present invention to provide a method, wherein two parts of a component are assembled together in a mold whereby one part is previously formed and subjected to the injection temperature and pressure during the molding of the second part which causes the one part to begin to melt, thereby causing fusing of the interengaging portions of both parts. The invention will be further described on the hand of a non limitative example under reference to the appended drawing Figures, wherein: - Figure 1 shows a cross-sectional view of a valve already briefly given as example in the text hereabove. - Figure 2 shows a view looking downwardly onto the valve seat to the valve, also showing the relationship between the valve guide and outwardly extending housing guide ribs. - Figure 3 shows a perspective view of the specific component of the present invention. - Figure 4 shows a view looking downwardly with respect to the view of Figure 3. - Figure 5 shows a cross-sectional view along the line V-V of Figure 4. - Figure 6 shows a cross-sectional view along the line VI-VI of Figure 4. While the heart of the present example consists of the method of assembling a valving plate to the valve guide, it is believed instructive to describe, in great detail, the valve assembly, which is the environment of use of the component assembled according to the invention. In this regard, attention is first directed to Figures 1 and 2 wherein a valve assembly is generally designated by the reference numeral 10 and is seen to include a valve body 1 1 , a cover 13 and a coupling member 15. The coupling member 15 includes a generally cylindrical outer wall 17 having a bottom termination 19 including an upwardly extending generally frusto-conical portion 21 which may be flexed inwardly or outwardly from the position shown in Figure 1 to accommodate to vent pipes of varying sizes. In Figure 1 , the vent pipe is generally designated by the reference numeral 9 and, as should be understood, is interconnected into a plumbing system of a home or building. The coupling member 15 also includes outwardly extending ring-like projections 23, 25 and 27 which are designed to facilitate coupling of the valve assembly 10 within a vent pipe rather than in surrounding relation thereto as shown in Figure 1. Thus, the coupling member 15 provides versatility in allowing the inventive valve assembly 10 to be coupled either within or in surrounding relation to a vent pipe of a plumbing system. As shown, in Figure 1 , the coupling member 15 is mounted in surrounding relation to a generally cylindrical portion 29 of the housing 1 1 which portion 29 contains a chamber 31 intended, as shown, to be fluidly coupled to the vent pipe 9. The portion 29 extends upwardly including a generally frusto-conical inward taper 33 and a further generally cylindrical portion 35 terminating, upwardly, in an inner annular valve seat 37 which comprises a generally circular annulus having an arcuately shaped bead-like configuration. An outer annular valve seat 39 is also provided in the valve housing 1 1 supported in outwardly spaced configuration with respect to the inner annular valve seat 37 by a series of fins 41 as seen in Figures 1 and 2. As best shown in Figure 2, in this example, six support fins 41 are provided. As shown in Figure 1 , the support structure of the housing 1 1 immediately outwardly adjacent to the outer annular valve seat 39 includes a shoulder 43 which is designed to allow firm support for the cover 13. The bead 45 is formed by sonically welding the cover 13 in assembled relation over the shoulder 43 of the housing 1 1 in the position shown in Figure 1. An O-ring can be used in larger versions of the breaker valve between the cover and shoulder 43. Screens 47 and 49 are provided at the locations shown to prevent passage of vermin such as rodents, bugs, or debris. Any suitable attachment means may be employed to hold the screens 47 and 49 in their assembled locations as particularly shown in Figure 1. As should be understood from Figure 1 , the screens 47 and 49 have extremely large openings large enough to allow unrestricted air flow through the valve housing 1 1 while being small enough to prevent passage of large debris, rodents or other vermin. The valve head of the present invention is generally designated by the reference numeral 50 and is seen to include a a valving plate 51 and a valve guide 53. With particular reference to Figure 3, it is seen that the valving plate 51 comprises an annular ring- like device and is made of a styrene-ethylene-butylene block copolymer which is a soft resilient flexible elastomer. The valve guide 53 is made of a acrylonitrile-butadiene-styrene copolymer which is a hard thermoplastic material. It includes a ring 55 engaging the surface 54 of the valving plate 51 and a plurality of lugs 57 extending upwardly with respect to the ring 55 in the view shown in Figure 3 , although, in practice, the valve head 50 is oriented upside down with respect to the view of Figure 3 as should be clearly understood from Figure 1. The orientation shown in Figure 3 is merely provided for clarity in understanding the particular structure of the valve head 50. Variations of the valve guide 53 can have one or more lugs 57. With reference to Figures 2 and 4, it should be understood that each guide lug 57 had an inwardly directed slot 59 designed to be slidably received on exterior surfaces of guiding ribs 36 formed on the exterior walls of the cylindrical portion 35 of the valve housing 1 1. This relationship is best shown in Figure 2. In the operation of the valve assembly 10, the coupling member 15 is utilized to couple the valve assembly 10 over the vent pipe 9 of a plumbing system. When a toilet is flushed in the plumbing system, this causes a suction in the direction of the arrow 8 and a reduction of pressure within the chamber 52 above the valving plate 51 so that the valving plate 51 is exposed to atmospheric pressure on its surface 54 and less than atmospheric pressure on its surface 56. This pressure differential causes the valving plate 51 to elevate with respect to its position as shown in Figure 1 allowing atmospheric air to enter in the direction of the arrows 12 and to flow in the direction of the arrow 8 until such time as the pressure within the vent pipe 9 is equal to atmospheric pressure, whereupon the pressures on the surfaces 54 and 56 of the valving plate equalize and gravity causes the valving plate 51 to resume its position as shown in Figure 1. As pointed out above, the present invention, which consists in a new method for assembling two parts, is illustrated here by the assembly of the valve head 50. In assembling the valve head 50, first the valve guide 53 is separately manufactured. The valve guide 53 is molded in any suitable manner of a copolymer of acrylonitrile- butadiene-styrene. The surface of the mold in contact with the top surface 58 of the valve guide 53 is sand blasted. Thereafter, the valve guide 53 is placed in another mold and the soft elastomer on the basis of a styrene-ethylene-butylene block copolymer is injection molded to form in the mold the soft valving plate 51. The surface 54 of the valving plate 51 is engaged with the top surface 58 if the valve guide 53. The top surface 58 of the valve guide is roughened because of contact with a sand blasted portion of its mold. The rough top surface 58 enhances fusion between such surface 58 and valving plate 51. The second mold used to form the valving plate 51 and simultaneously fuse it to surface 58 should have a top surface sand blasted or treated with a mold release agent to enhance release of the valve head 50 from the mold without deforming the valving plate 51. In this orientation, the valve guide 53 and valving plate 51 are heated by the injection temperature of the soft elastomer which is in excess of 200°C and subjected to the injection pressure which is about 1000 bar. Consequently a thin layer of the surface 58 of the valve guide 53 melts and thereby fuses with the surface 54 of the valving plate 51 at 62 (Figure 5). When this melting and fusing has taken place, the assembled valve head 50 is allowed to cool resulting in the valve head 50 as used in accordance with the example of the present invention. Through assembly using this method, the valving plate 51 is maintained in permanent interconnection with the valve guide 53 regardless if the corrosive nature of the environment in which the valve head 50 operates or the degree of humidity thereof. This method of assembly of the valve head 50 has proven to be far superior to any other methods known including use of adhesives, bolting or other means of connection. As such, the method of assembly has been disclosed on the hand of a valve. It is clear that the new proposed method can be used for a large variety of applications and in particular in any case where a hard thermoplastic material should be firmly secured to a soft elastomer material of particular shape. The description of the valve hereabove is only given by way of example, various changes, modifications and alterations in the teachings of the present invention may be contemplated by those skilled in the art without departing from the intended spirit and scope thereof.

Claims: CLAIMS 1. Method for manufacturing by molding a component composed partly of a hard thermoplastic material and partly of an soft elastomer material characterized by following steps: - forming first the part of hard thermoplastic material; - placing the first part in a mold capable to receive the soft elastomer material; - injection molding the soft elastomer (second) part and simultaneously engaging the surface A (to be assembled to the second part) of the first part to the surface B (to be assembled to the first part) of the second part and subjecting the surface A to the injection molding temperature and pressure whereby the surface A is softened and consequently both surfaces A and B are fused together. 2. The method according to claim 1 , characterized in that the hard thermoplastic material is a material chosen from the group formed by hard polypropylene, hard polyvinylchloride and an acrylonitrile-styrene copolymer, when useful reinforced with fibers. 3. The method according to claim 2, characterized in that the hard thermoplastic material is an acrylonitrile-butadiene-styrene copolymer. 4. The method according to claim 1 , characterized in that the soft elastomer is a material chosen from the group formed by synthetic rubbers, silicone elastomers, soft vinyl or urethane polymers, butadiene polymers or copolymers, sulfonated polyethylene, soft styrene copolymers. 5. The method according to claim 4, characterized in that the soft elastomer is a copolymer of styrene-ethylene and butadiene- styrene. 6. The method according to claim 1 , characterized in that the surface A has been roughened. 7. The method according to claim 6, characterized in that the roughened surface is formed by molding the first part of thermoplastic material in a mold where the portion of the mold corresponding to surface A has been sand blasted. 8. The method according to claim 1 , characterized in that the surface of the mold in which the second part is formed is sand blasted prior to receive the soft elastomer to enhance release from the mold without deforming this second part. 9. A valve assembly manufactured according to the method of any of the preceding claims, characterized in that it includes a valve housing with an inlet port, an outlet port and a valve seat therebetween, a valve guiding structure and a valve head movable between a closed seated position on the valve seat and an open position spaced therefrom, whereby said valve head includes a valving plate, made of soft elastomer, engageable with the valve seat and a valve guide made of hard thermoplastic material and heat fused to said valving plate in the mold wherein the valve plate is formed and wherein the valve guide is interengageable with the valve guiding structure to guide movements of the valve head. 10. A valve assembly according to claim 9, characterized in that the valve guide is made of an acrylonitrile-butadiene-styrene copolymer and the valve plate is made of a styrene-ethylene-butylene block copolymer.

Inventors: CHALICH DANIEL, ERICSON KURT STURE BIRGER, CHALICH, DANIEL, ERICSON, KURT, STURE, BIRGER
Applicants: CHALICH DANIEL, ERICSON KURT STURE BIRGER, CHALICH, DANIEL, ERICSON, KURT, STURE, BIRGER
Application year: 1994
Main classification: B29C45
IPC codes: B29C45, B29D31, F16K15